ORA-12514: TNS:listener does not currently know of service requested in connect

it can be one of these

• check database status for single instance and CDB and PDB status for multitenant
• srvctl status database -d dbname or show pdbs from sqlplus
• check services status with – srvctl status service -d dbname
• check OUD or TNS entry for correct service name
• check remote_listener parameter – show parameter remote_listener
• check PDB name